Eight samples of effluent from a pulp mill were each divided into 10 batches. From each sample, 5 randomly selected batches were subjected to a treatment process intended to remove toxic substances. Five fish of the same species were placed in each batch, and the mean number surviving in the 5 treated and untreated portions of each effluent sample after 5 days were recorded and are given in Table 5.20. Test to see whether the treatment increased the mean number of surviving fish. 

Table 5.20 Data for Exercise 14. MEAN NUMBER SURVIVING Sample No. Untreated Treated 1 2 3 4 5 55 1 1.8 1 3.6. 5 5 5 1.2 4.8 5 16 55 7 2.6 4.4. 8 12